1. Field of the Invention
The present invention relates to a plating apparatus for plating a substrate such as a semiconductor wafer with copper, a copper dissolution tank and a cartridge for use in the plating apparatus, and a plating method.
2. Description of Related Art
In the production of a semiconductor device, a plating process is often performed for plating one surface of a semiconductor wafer (hereinafter referred to simply as “wafer”). A typical plating apparatus for plating a wafer with copper includes a plating vessel which contains a copper-ion-containing plating liquid to be brought into contact with one surface of the wafer, a dissolvable copper anode disposed in the plating vessel, and a cathode to be brought into contact with the wafer. Such a plating apparatus is disclosed in U.S. Pat. No. 6,258,220B1.
For the plating, the cathode is kept in contact with the wafer, and one surface (lower surface) of the wafer is kept in contact with the plating liquid filled in the plating vessel. In this state, the anode and the cathode are electrically energized. Thus, electrons are donated to copper ions in the plating liquid in an interface between the plating liquid and the wafer, so that copper atoms are deposited on the surface of the wafer. On the other hand, copper atoms of the anode are deprived of electrons to leach in the form of copper ions into the plating liquid in an interface between the anode and the plating liquid. The anode functions as a copper supply source for supplying copper ions to the plating liquid.
Thus, copper ions are consumed in the plating liquid to be deposited in the form of copper atoms on the wafer, while being supplied in the corresponding amount from the anode. Therefore, the amount of copper ions in the plating liquid is kept virtually constant.
However, the anode of the plating apparatus is consumed during the repetitive plating process, requiring replacement. The plating vessel has a small size, which is determined according to the size (diameter) of the wafer to be treated. Further, the anode has a relatively great weight. Therefore, the replacement of the anode disposed at a great depth in the plating vessel is laborious.
The plating apparatus is generally disposed in a clean room. Therefore, the clean room is likely to be contaminated with copper due to the scattering of the plating liquid when the anode is replaced. Unintended contamination with copper in other process steps results in deterioration of the characteristics of the device (product). Particularly, a plating liquid containing copper sulfate is liable to cause contamination when it is dried to form powder dust.
When the anode is replaced, the inside of the plating apparatus is exposed to the atmosphere in the clean room. Therefore, the inside of the plating apparatus is also contaminated. Particularly, where the cleanliness of the inside of the cleaning apparatus is set higher than the cleanliness of the clean room, the quality of the product is remarkably deteriorated by the contamination of the inside of the plating apparatus.
The plating process is stably performed only with the surface of the copper anode being covered with a so-called black film. However, the formation of the black film requires preliminary electrical energization after the replacement of the anode. This prolongs the downtime of the apparatus, thereby reducing the capacity utilization rate of the apparatus.
Further, the state of the black film is stabilized only when the anode is electrically energized in the same cycle. However, the plating apparatus is rarely operated in a constant cycle, but is sometimes out of operation. The black film is deteriorated when the plating apparatus is out of operation. Therefore, when the operation of the plating apparatus is thereafter resumed, the plating process cannot properly be performed, reducing a product yield.
Further, slime is often generated from the black film on the surface of the anode. The black film and the slime are liable to be separated from the anode to contaminate the plating liquid. This may adversely affect the plating process. A conceivable approach to the prevention of the adverse effect is to cover the anode with a filter. However, it is difficult to completely cover the anode with the filter, because the anode has a connector for connection to a power source. Where the anode is covered with the filter, the replacement of the anode is more difficult.